Fig. 3. Extracellular pH change demonstrated by Bromocresol Purple (pH 5.2, yellow; pH 6.8, purple). (A) Alkalinization of extracellular space in the outer zone, t=1 h, 7 min. The arrow shows a position partially deprived of cells to show the change in color more clearly. (B,C) A drop of Bromocresol Purple solution (left) kept at a distance from a 2-D cell mass (right) also changes color after (B) t=15 min and (C) t=2h, 44 min. Scale bars, 100 µm (A); 1 mm (B,C).